The main methods for reducing fluoride in water treatment

The main methods for reducing fluoride in water treatment

The main methods for reducing fluoride in water treatment include anion exchange resin, activated carbon adsorption, activated alumina adsorption, bone charcoal (calcium carboxyphosphate) adsorption, electrodialysis, reverse osmosis, etc. Today we will compare these commonly used methods one by one and select the more suitable one for you.

1. Anion resin ion exchange method:
Anion resin has a high energy for removing anions from water, but its efficiency in removing fluoride ions is very low. This is because the selection order of anion resin is sulfate>chloride>bicarbonate>fluoride, with fluoride ranking last. Therefore, the efficiency of fluoride removal is very low, and the price is expensive. Regeneration is extremely complex and difficult to manage, and it is rarely used. In recent years, China has introduced zirconia anion resin from Japan, which has a very good fluoride removal effect and high energy. It can remove 250000 mg of fluoride per kilogram, but the price is 450000 yuan/ton, and it cannot be regenerated. However, the cost of purifying water is more than 4 yuan per ton, which is not suitable for China's national conditions.

2. Activated carbon adsorption method:
Activated carbon has a particularly large specific surface area, but its pore size is also very large. After the fluoride ions enter the pores, the fluoride ions that enter earlier are easy to escape, so the adsorption capacity for fluoride ions is very low, and it cannot be regenerated. After adsorption saturation, it can only be discarded. High operating costs are generally not acceptable.

3. Carboxyl calcium phosphate adsorption method:
Carboxyl calcium phosphate has a large adsorption capacity for fluoride, which was adopted by many water plants in China in the 1970s and 1980s. Its shortcomings include high material prices; Secondly, it has poor strength and is prone to breakage; Thirdly, the operation is complex and the management difficulty is very high, especially during regeneration. Poor control of the regeneration concentration can cause material breakage and failure, and replacing one ton of material costs tens of thousands of yuan; The fourth issue is that the effluent has a fishy odor, poor taste, and even the possibility of exceeding ammonia nitrogen standards. These drawbacks limit its application and are currently rarely adopted.

4. Activated alumina adsorption method:
This method is currently the most widely used method in China, and it is unanimously believed that activated alumina is the most effective method for reducing fluoride. Currently, about 60% of defluorination points in China still use activated alumina, which is also the most commonly used defluorination agent in the world.

5. Electrodialysis method:
This method is a fluoride removal method for ionizing substances in water using electrode aluminum plates. The fluoride removal is clean and thorough, the effluent quality is good, it can be automated, and the management is relatively easy. The disadvantage is that the investment is high and the operating cost is too high. The electrodialysis method is also known as the electric tiger, and the electricity cost is extremely high, which the general economic conditions cannot afford.

6. Reverse osmosis method:
This method is clean and thorough in removing fluoride, with good effluent quality. Its disadvantages are similar to electrodialysis, with high operating costs ranging from 1.5 yuan to 2 yuan per ton of water, and low average water production rate. For every ton of water purified, 0.25-0.6 tons of water need to be discarded. For a 4800 ton water plant, 1500 tons of water need to be discarded per day. Therefore, reverse osmosis is currently only suitable for industrial high-purity water preparation and bottled and barreled water, and is not suitable for large and medium-sized water plants.  ---B